The present invention relates to waveguides such as radio frequency (RF) structures, and more specifically, to RF structures for superconducting quantum computing circuits and chip mode isolation and cross-talk reduction implementing buried metal layers and through-vias.
Quantum computing using superconducting elements uses resonant structures such as coplanar waveguides and capactively shunted Josephson junctions to store and manipulate information. These structures are built using conventional semiconductor manufacturing methods onto substrates such as Si wafers. A chip is diced out of a full wafer and then cooled and tested. This chip can support various resonant electromagnetic modes determined by the size (dimensions) of the chip. For chips in the several millimeter size range, these modes can be in the several GHz range, which is similar to the frequencies of the structures built on the chip and can therefore cause problems. RF structures used in superconducting quantum computing circuits need to be isolated from spurious resonant systems in order to maintain coherence, and in addition have to be isolated from other RF structures on the same chip. RF modes in the substrate itself can cause issues in this regard, both as a source of loss in the qubit (due to mode coupling), and also as an unintended conduction path between nominally separate structures.
Implementation of superconducting circuitry is seen as one of the strongest candidates to realize to enable quantum computing. The presence of chip modes is responsible for degradation of performance through the damping of qubit resonances and by the increase of crosstalk between circuit elements on-chip.